1. Field of the Invention
The invention relates to mechanisms for securing one object to another. More particularly, this invention relates to mechanisms that secure screen panels to a support structure used to vibrate and separate materials such as aggregates that are placed on the screen modules.
2. Description of Related Art
In the mining and aggregates industries, aggregates are excavated from the ground in large quantities that contain both desired material and undesired material mixed together. The aggregates are separated into desired product lines and any undesired materials are removed. One common method for achieving the separation utilizes a large porous surface, or screen, on which the combined excavated material is placed and sifted. The screens are usually secured to a frame-like structure upon which vibration-type forces are mechanically exerted such that the materials on the screens are shaken, causing certain of the material to filter through the pores of the screen. The repetitive and sometimes excessive forces exerted by the support structure require that the screens be securely affixed so that they do not come loose from the structure.
The screens are usually made of durable material to withstand the repetitive impacts and abrasive forces caused by the bouncing and shaking of the aggregates, which are usually comprised of hardened materials of various shapes and sizes. Even though made of durable material, the screens experience wear and sometimes failure that require replacement. Because the wear or failure is often in an isolated location, screens are frequently comprised of individual panels, or modules, that permit a failed or worn module to be replaced. Relatedly, it is a common practice in the industry to rotate the screen modules to minimize the isolated wear that would otherwise result to an individual screen module. Such rotation of screen modules usually increases the life-span of each module. Without the ability to exchange individual modules, an entire screen surface would have to be replaced even though only a small or isolated portion of the surface had been damaged.
Likewise, it is often necessary to exchange an entire screen grid in order to alter the size aggregate the owner seeks to collect. For all these reasons, it is desirable that the screen modules be securely attached to the support structure while at the same time permit removal and reattachment with relative ease and without causing damage to the screen module locking mechanism.
In such multi-paneled systems, each screen module is usually secured to a support frame and is mated with other compatibly shaped and sized screen modules to form a continuous surface, or grid. Various methods for securing the modules to the support frame have been disclosed and are known in the prior art. Likewise, various methods for mating each module to other compatible modules have been disclosed and are known in the prior art.
Such previously disclosed methods often employ protrusions that extend from the underside of the screen module that fasten by various means to the support frame, often through apertures within the frame. In one prior art embodiment, the protrusions have an annular ridge, the diameter of which slightly exceeds the diameter of the aperture of the support frame that will receive the protrusion. As the protrusion of the screen module is forced through the aperture in the support frame, the ridge interlocks with the underside of the support frame. To enable the ridged protrusion to fit through the slightly smaller aperture and still achieve a locking relationship with the support frame, the protrusion is commonly made of “resiliently deformable material.” Examples of such locking protrusions in the prior art are disclosed in Freissle, U.S. Pat. Nos. 4,716,694 and 5,664,685. Various other locking systems have been disclosed in Hassall, U.S. Pat. No. 4,219,412, Schmidt, U.S. Pat. No. 4,383,919, and elsewhere.
Those skilled in the art will appreciate that the use of deformable material such as polyurethane or rubber also allows the unlocking and removal of the screen module from the support frame, but this often occurs with substantial difficulty and can result in damage to the screen module. As is disclosed in Freissle, to remove the screen module, it is usually necessary to apply significant external force in such a manner as to cause the temporary deformation of the protrusion in order to permit its removal from the aperture of the support frame. It will be appreciated that if the person who is responsible for removing the screen module does not exercise appropriate care, permanent damage to the screen module can result rendering the screen module useless.
Another limitation of existing systems occurs because the use of deformable material can lead to compromised locking relationships between the screen module and the support frame. By its very nature, deformable material permits changed shapes—however slight—especially as outside forces act on the material. If such forces are either acute or occur repetitively over time—such as the severe vibration forces exerted by the shaking support frame—deformation of the material can result and can deprive the protrusion of its ability to restrain effectively the screen module against the support frame.
To guard against this sudden or gradual deformation problem, those skilled in the art have often fashioned the locking protrusions using increasingly hardened materials. Of course, increasing the rigidity of the materials necessarily increases the difficulties for attaching and unlocking the screen modules, thereby increasing the likelihood of damage to the system, as well as inefficiencies, during the replacement process.
Another technique commonly used by those skilled in the art in their efforts to address these problems involves the employment of removable pins inserted within protrusions creating outward pressure causing the protrusions to engage the support frame. One such example of this technique is disclosed in Galton, U.S. Pat. No. 5,049,262. Although the pins can be removed thus permitting the screens to be disengaged, such pins can be difficult to handle and are susceptible to being dropped or lost. The pins themselves are susceptible to coming loose by virtue of the vibrational forces of the system.
As a result, there is a need for a locking system that provides increased restraint capabilities between the screen module and the support frame, while at the same time permitting relatively simple and efficient removal and replacement of the screen modules without causing damage to the screen module or the support frame.